1. Field of the Invention
The present invention relates to a swingable vehicle.
2. Description of Background Art
Hitherto, a swingable vehicle is known wherein a slide type triport joint is used at one end of a drive shaft for being connected between a final speed reduction gear and a wheel. See, Japanese Utility Model Laid-open No. Sho 63-43905.
FIG. 1 of Japanese Utility Model Laid-open No. Sho 63-43905 will be described referring to FIG. 15 of the present specification. However, the reference numeral have been changed.
FIG. 15 is a side view of a drive shaft for a swingable vehicle according to the prior art, wherein a slide type triport joint 404 is used on the wheel 402 side of a drive shaft 403 for connection between a final speed reduction gear 401 and a wheel 402. A fixed type Birfield joint 405 is provided on the final speed reduction gear 401 side of the drive shaft 403.
The slide type triport joint 404 is a constant velocity joint in which the inner circumferential surface of a sleeve 407 is formed as one body with a spindle 406 being provided with three axial-direction grooves 408. Three radial-direction leg portions 411 are provided at an end portion of the drive shaft 403 and are axially movably engaged with the axial-direction grooves 408.
In the slide type triport joint 404, since the engagement portion between the axial-direction grooves 408 and the radial-direction leg portions 411 is located at a deep position of the inner circumferential surface, the bend angle of the slide type triport joint 404, i.e., the angle between the axis of the spindle 406 and the axis of the drive shaft 403 cannot be made large. In order to secure a vertical stroke of the wheel 402, it is necessary to secure the overall length of the drive shaft 403. Therefore, even in the case of a small vehicle where it is desirable to reduce the vehicle width, a reduction in the vehicle width is limited due to the need to secure the vertical stroke.
In addition, the limitation as to the bend angle of the slide type triport joint 404 causes limitations as to the freedom in design, such as specifications, size and layout, of the suspension in the vehicle. In addition, in the case of using the slide type triport joint 404 for a swingable vehicle, for example, the bend angle may limit the swing angle.
Furthermore, in the slide type triport joint 404, the processing of the axial-direction grooves 408 in the sleeve 407 and the formation of the radial-direction leg portions 411 on the drive shaft 403 involves difficulties. Therefore, the slide type triport joint 404 is higher in cost than the above-mentioned fixed type Birfield joint 405, for example.
A vehicle frame structure is also known in the related art wherein a rear wheel is attached via swing arms as disclosed in Japanese Utility Model Registration No. 2521705.
FIG. 1 in Japanese Utility Model Registration No. 2521705 will be described below in conjunction with FIG. 16 of the present specification. In addition, and FIG. 3 in Japanese Utility Model Registration No. 2521705 will be described below in conjunction with FIG. 17 of the present specification. In FIG. 16, only the rear half of the vehicle is shown. Reference numerals have been renumbered.
FIG. 16 is a side view showing a vehicle flame structure in the related art. A seat mounting frame 1402 and an engine supporting frame 1403 are mounted on top of the rear portion of a main frame 1401 of a sitting-type four-wheel buggy. An inclined frame 1404 is attached so as to bridge between the rear end of the main frame 1401 and the engine supporting frame 1403. A rear frame 1406 of an L-shape in side view is attached to the rear end of the engine supporting frame 1403 and a lower frame 1407 is attached so as to bridge between the end of the rear frame 1406 and the main frame 1401.
An engine 1408 is provided together with a transmission 1411 that is connected to the rear portion of the engine 1408. A differential gear 1412 is connected to the rear portion of the transmission 1411 and the differential gear 1412 is attached to the rear frame 1406.
FIG. 17 is a plan view of a principal portion showing the vehicle frame structure in the related art. Rear swing arms 1416 are attached to the lower frame 1407 via brackets 1414, 1414 with an axle pipe 1417 integrally attached to the rear swing arms 1416. An output shaft 1418 extends from the differential gear 1412 and is rotatably supported by the axle pipe 1417. A rear wheel 1421 is attached to the extremity of the output shaft 1418.
In FIGS. 16 and 17 the lower frame 1407 limits ground clearance and limits the downsizing of the frame when it is applied to a small vehicle.
Further, a swingable vehicle is known wherein one drive gear is suspended from a vehicle and the left and right wheels are inclined in conjunction with each other. See, for example, FIGS. 10 and 11 of Japanese Patent Laid-Open No. Sho 61-125973.
As another swingable vehicle, there has been known a three-wheel vehicle in which two rear wheels are respectively supported by rear forks. See, for example, FIGS. 1 and 9 of Japanese Patent Laid-Open No. Sho 61-125973.
The swingable vehicle disclosed in FIGS. 10 and 11 of Japanese Patent Laid-Open No. Sho 61-125973 is a vehicle in which the left and right wheels are moved in conjunction with each other. However, in the case where the vehicle speed is raised or where the condition of the road surface varies greatly, it is desirable that the left and right wheels be suspended independently.
On the other hand, FIG. 1 of Japanese Patent Laid-Open No. Sho 61-125973 discloses a swingable vehicle of an independent suspension type in which the left and right wheels are supported by the rear forks.
FIG. 1 and 7 of Japanese Patent Laid-Open No. Sho 61-125973 will be described referring to FIGS. 20(a) and 20(b) below. In addition, the condition where the three-wheel vehicle is inclined will be described referring to FIG. 20(c). The plan view in FIG. 1 of Japanese Patent Laid-Open No. Sho 61-125973 is omitted. In addition, the reference numerals have been changed.
FIGS. 20 (a) to (c) illustrate a conventional swingable vehicle, wherein FIG. 20(a) is a side view of a three-wheel vehicle as the swingable vehicle, showing the condition where a left-right pair of rear forks 1502 and 1503 are vertically swingably mounted to a differential device 1501 provided at a lower portion of the three-wheel vehicle. Rear wheels 1504 and 1505 are rotatably mounted to rear end portions of the rear forks 1502 and 1503. In addition, chains 1506 and 1507 are provided for transmitting power from the differential device 1501 to the rear wheels 1504 and 1505.
FIG. 20(b) shows the condition where of the rear wheels 1504 and 1505 is positioned on a projecting portion of the road surface. T1 in the FIG. 20(b) denotes the tread between the rear wheels 1504 and 1505.
FIG. 20(c) shows the condition of the rear wheels 1504 and 1505 when the three-wheel vehicle is swung. In this case, while the distance between the rear wheels 1504 and 1505 is T1, the distance between the respective grounding points of the rear wheels 1504 and 1505 is T2, and T2>T1. Namely, the tread between the rear wheels 1504 and 1505 is substantially broadened. Moreover, the distance T2 varies depending on the leftward or rightward swing angle of the three-wheel vehicle. As a result, the turning performance varies during turning.
In addition, in the conventional swingable vehicle of the left and right independent suspension type, and in FIG. 20(a), the chains 1506 and 1507 need maintenance such as length adjustment and replacement. Further, the wild ground operating performance of the three-wheel vehicle is enhanced if the vertical stroke amounts of the rear wheels 1504 and 1505 can be enlarged.